Differential Diagnosis for Rash Involving Few Scattered Small Erythematous Papules on Back of Neck

• Single Most Likely Diagnosis
  • Contact Dermatitis: This is a common condition that occurs when the skin comes into contact with an irritant or allergen, leading to a rash. The back of the neck is a typical area for contact dermatitis due to exposure to allergens or irritants from clothing, jewelry, or hair products.
• Other Likely Diagnoses
  • Atopic Dermatitis (Eczema): Characterized by itchy, inflamed skin, atopic dermatitis can present with erythematous papules and is common in areas like the neck.
  • Pityriasis Rosea: An infectious condition that starts with a single patch (herald patch) followed by a widespread rash, including small erythematous papules, often on the trunk and sometimes the neck.
  • Folliculitis: Inflammation of the hair follicles, which can appear as small, erythematous papules or pustules, commonly found on the neck, especially in areas where the skin is irritated or where there is excessive sweating.
• Do Not Miss Diagnoses
  • Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a rash (though typically more widespread and petechial or purpuric rather than just erythematous papules). Early recognition is crucial due to its high mortality rate if not promptly treated.
  • Lyme Disease: Caused by Borrelia burgdorferi, transmitted by tick bites. The initial stage can present with a characteristic "bull's-eye" rash (erythema migrans), but in some cases, the rash might appear differently, including as scattered erythematous papules.
• Rare Diagnoses
  • Sarcoidosis: A condition that can affect multiple parts of the body, including the skin, where it may cause erythematous papules among other skin manifestations.
  • Guttate Psoriasis: A type of psoriasis that appears as small, dot-like lesions, often on the trunk, and can sometimes be found on the neck. It's less common than plaque psoriasis but should be considered in the differential diagnosis of a rash with erythematous papules.